Every effort has been done for long years for higher sensitization and reduction of residual colors after processing of silver halide photographic materials. It is known that sensitizing dyes used for spectral sensitization have a great influence on photographic capabilities of a silver halide photographic material. A slight structural difference of sensitizing dyes largely affects photographic capabilities such as sensitivity, fog or storage stability but it is difficult to estimate the effects in advance, therefore, many engineers have endeavored to synthesize various kinds of sensitizing dyes and examine photographic capabilities thereof. However, photographic capabilities cannot be forecast yet up to date.
From the above reasons, techniques for spectrally sensitizing silver halide highly sensitively without generating mal-effects, such as fog, have been demanded.